The present invention relates to method and apparatus which is particularly useful in connection with the detection of intrusion into a space to be protected and is particularly useful in detecting, for example, the opening of a window, the breaking of a window or even a sudden impact on the walls of the area.
Heretofore, intrusion detection has been accomplished primarily by means of audio detectors which detect the occurrence of a sound. In more sophisticated form the detectors can be tuned to detect sounds at specific frequencies such as the frequency of the sound made by the breaking of a pane of glass, the slamming of a door or other occurrences. The difficulty with audio discriminator detectors is that in general, there are other occurrences which generate sounds in the same frequency as the frequency generated by the occurrence to be detected thus leading to false trips and false alarms.
Infrared detectors are sometimes utilized as intrusion detectors but do not detect the occurrence surrounding the intrusion, such as the breaking of glass or the opening of a door nor do they detect the events which can occasion the generation of a low frequency pressure wave.
No prior art device is known utilizing a change in pressure as indicated by the occurrence of a low frequency pressure wave in the area to be protected as the basis for the detection of the selected occurrence involving change in the physical characteristics of the area to be protected. Furthermore no prior art devices are known wherein a pressure transducer is utilized to detect the occurrence of a low frequency pressure wave in an area to be detected accompanied by a specific sound occurrence such as the breaking of glass, etc.